GlobalPost reported that Foley's parents received an email on Aug. 12 from the militants saying that he would be executed.

"You were given many chances to negotiate the release of your people via cash transactions as other governments have accepted," the email said. "We have also offered prisoner exchanges to free the Muslims currently in your detention ... however you proved very quickly to us that this is not what you are interested in."

GlobalPost reported that it decided to publish the email in the interest of transparency to tell Foley's story.

Foley was a freelancer at GlobalPost when he was kidnapped on Thanksgiving Day in 2012.

"You do not spare our weak, elderly, women or children so we will not spare yours," the email said. "You and your citizens will pay the price of your bombings. The first of which being the blood of the American citizen, James Foley. He will be executed as a direct result of your transgressions toward us."

The militants for months had demanded $132.5 million from Foley's parents and political concessions from Washington, but received neither.

United States officials also revealed that they had tried to rescue Foley and other captives earlier in the summer in a special military operation, but the special forces from units such as Delta Force and Navy SEAL Team 6 failed to find them.

At a news conference outside Foley's Rochester, New Hampshire, home, Foley's parents, Diane and John, broke down several times speaking of their son.